This invention relates to current detectors, more specifically to that employing a semiconductor Hall-effect device for obtaining a voltage proportional to the magnitude of the current detected. Still more specifically, the invention deals with how to improve the noise immunity of this kind of current detector.
By the term xe2x80x9cHall-effect devicexe2x80x9d used herein and in the claims appended hereto is meant the voltage generator built on the familiar Hall effect to give an output voltage in direct proportion to the magnetic field applied. Disposed contiguous to a current path, the Hall-effect device will be subjected to the magnetic field that is generated in proportion to the magnitude of the current flowing through the path. The result will be the production of a voltage proportional to the current magnitude.
The instant applicant proposed in PCT/JP99/05408 a current detector in which an insulating film is formed upon a semiconductor Hall-effect device and, on this insulating film, a conductor layer for carrying a current to be detected. The current path is thus situated as close as feasible to the Hall-effect device, resulting in enhancement of the sensitivity of the current detector.
This prior art current detector proved to be unsatisfactory, however, in its noise immunity. It was equipped with no means designed explicitly for protection of the device against production of spurious voltage signals due to external disturbances.
The present invention seeks to enhance the noise immunity, and hence the reliability of operation, of the current detector of the type defined.
Stated in brief, the invention concerns a semiconductor current detector comprising a semiconductor substrate having a Hall-effect device formed therein from one surface thereof, the Hall-effect device having a plurality of semiconductor regions including a primary working region for generating a Hall voltage proportional to the magnitude of a current or to be detected or measured. A conductor strip is formed over said one surface of the semiconductor substrate via insulating means so as to extend around at least part of the primary working region of the Hall-effect device, for carrying at least a prescribed fraction of the current to be translated into the Hall voltage. A shielding layer is formed in the insulating means for shielding the Hall-effect device from external disturbances.
Typically, the insulating means is a lamination of three insulating layers. Electrodes, as well as conductor strips joined thereto, are formed on a first insulating layer which directly overlies the semiconductor substrate. The shielding layer is formed on part of a second insulating layer which overlies the first insulating layer. The conductor strip is formed on a third insulating layer overlying the second insulating layer.
The above arrangement of the three insulating layers in relation to the shielding layer and other components of the current detector is not a requirement. Alternatively, for instance, the shielding layer may be provided on the third insulating layer, and the conductor strip between the second and the third insulating layer. As a further alternative, a fourth insulating layer may be provided over the third insulating layer, and a second shielding layer on this fourth insulating layer.
Shielded by one or more shielding layers as above, the current detector will detect currents without errors due to external disturbances. The shielding layer or layers, as well as the current-carrying conductor strip, are integrally built into the semiconductor current detector, so that no substantial increase in size results from the addition of the shielding layer or layers. The integration of the conductor strip with the Hall-effect device is desirable by reason of their unvarying positional stability, and hence a consistently high accuracy of detection, from one current detector to another.
The above and other objects, features and advantages of the invention and the manner of realizing them will become more apparent, and so the invention itself will best be understood, from the following description taken together with the attached drawings showing the preferred embodiments of the invention.